Spectral Characteristics And Water Content Estimation Of The Tidal Soil In Jiyang County

Soil water is an important component of soil,the key factor in the exchange of energy,the media of the movement of organic matter in the soil,an important index to measure the degree of soil drought,and also a necessary element for the growth of crops.The traditional method of soil moisture measurement has the disadvantages of small measuring point,slow speed,limited range.It can not meet the needs of large area soil moisture monitoring,and hyper-spectral remote sensing provides a new technique for quantitative monitoring of large area soil moisture content because of the advantages of high spectral resolution,multi band and abundant information.However,optical satellite remote sensing can only detect soil surface water content,and can not quickly monitor soil moisture content.Therefore,the study of the spectral characteristics of soil surface and the establishment of an indirect spectral estimation model for soil plough water content are of great significance for the rapid monitoring of soil water content and the development of fine agriculture by optical satellite remote sensing.This paper takes Jiyang County of Shandong Province as the research area.The paper takes 85 soil moisture information collected as research datas(5cm surface soil and 20cm plough layer soil)and the hyper spectral data of wave bands between250nm to 3500nm,and established multiple linear regression equation as the model to predict the soil water content,thus achieving the goal of predicting the plough layer soil water content.The main research contents and conclusions are as follows:(1)The spectral analysis of surface soil and tillage layer.The spectral characteristics of soil were analyzed by contrast analysis.The results showed that the outdoor spectrum of soil surface water content in Jiyang county and the outdoor spectrum of the water content in the plough layer were approximately the same in different water content.The spectral reflectance of soil decreased with the increase of water content,and the two was negatively correlated;the outer spectral reflectance of the surface layer was negative.The spectral reflectance of the soil is higher than that of the plough layer,but the spectral reflectance of the topsoil is higher than that of the surface soil at 1800nm to 1900nm.The spectral reflectance of the soil with different water content varies with the wavelength.In the short wave band,the soil spectral reflectance changes faster with the increase of soil moisture,while in the long wave part,the soil reflectance is reversed.The change of emissivity is relatively slow.(2)Characteristic band selection and feature factor extraction of moisture content in fluvo aquic soil of Jiyang County.Using various spectral transformation methods,such as square,square root,reciprocal,logarithm,first order differential equation and their combinations and analysing the correlation between the original soil spectra and the transformed ones,the sensitive bands of soil water content can be determined,and based on the maximal correlation,the characteristic factors are selected.The conclusions indicate that among the above transformations,The effect of square root transformation and logarithmic transformation of spectrum is better,and the maximum correlation coefficient is increased from 0.90 to 0.94.The effect of other transformation methods is not obvious.The first order differential transformation of the spectrum and the two order differential transformation only improve the spectral correlation in the visible light,but the maximum correlation of the spectrum is still not improved.The square and reciprocal transformation of spectra is of little help to improve the correlation between soil reflectance and soil moisture.In a comprehensive description,the spectral logarithmic transformation values of the soil surface spectra at 1339nm,1457nm,1745nm and 1968nm are selected as the characteristic factors of the surface spectrum,and the original spectral values of soil plough layer at 1347nm,1451nm,1775nm and 1956nm are the spectral characteristics of soil plough layer.(3)To establish the direct establish the model of plough layer soil water content.By comprehensive modeling analyses to establish the direct prediction model of plough layer soil water content and through the surface spectral data to predict the water content of plough layer soil water further to estimate R~2=0.85,the accuracy of the test model R~2=0.8397.The actual plough soil water content can be predicted,which is of paramount significance to agricultural production.